Rotational molding apparatus

ABSTRACT

A rotational molding apparatus comprising one or more annular tracks, a plurality of drive carriages traveling along said tracks, rotary molds each of which being supported by supporting means are coupled to said several carriages through the intermediary of said supporting means, rotatory mechanisms each of which transmits a rotational motion to a rotating shaft of each of said several molds from a drive source disposed in each of said carriages, a heating tunnel for each of said annular tracks, said tunnel housing a part of said annular track and permiting the passage therethrough of said carriages and molds, and a cooling tank for each said annular tracks, said cooling tank being provided in the course of the molds emerging from the heating tunnel after passage therethrough, said cooling tank being adapted to cool said molds as they pass therethrough. The apparatus is suitable for the mass production of synthetic resin molded articles of good quality with improved productive efficiency and ease of controlling production and heating temperature.

United States Patent Mori et a].

[ 51 July 18,1972

[54] ROTATIONAL MOLDING APPARATUS [72] Inventors: Hlsayuki Mori; Yoji Noguchl, both of Nara, Japan [73] Assignee: Seklsui Kegaku Ogyo Kabushiki Kaisha,

Osaka, Japan [22] Filed: June 2, 1970 [21] Appl.No.: 42,721

FOREIGN PATENTS OR APPLICATIONS 551,366 1/1958 Canada ..l8/26RR Primary Examiner-Robert L. Spicer, Jr.

Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT A rotational molding apparatus comprising one or more annular tracks, a plurality of drive carriages traveling along said tracks, rotary molds each of which being supported by supporting means are coupled to said several carriages through the intermediary of said supporting means, rotatory mechanisms each of which transmits a rotational motion to a rotating shaft of each of said several molds from a drive source disposed in each of said carriages, a heating tunnel for each of said annular tracks, said tunnel housing a part of said annular track and permiting the passage therethrough of said carriages and molds, and a cooling tank for each said annular tracks, said cooling tank being provided in the course of the molds emerging from the heating tunnel after passage therethrough, said cooling tank being adapted to cool said molds as they pass therethrough. The apparatus is suitable for the mass production of synthetic resin molded articles of good quality with improved productive efficiency and ease of controlling production and heating temperature.

8 Claims, 7 Drawing Figures Patented July 18, 1972 3,677,670

4 Sheets-Sheet 1 HISAYU'KI MORI and YOJI NOGUCHI,

INVENTORS Ill/W11 TTTQRNEY Patented July 18, 1972 3,677,670

4 Sheets-Sheet 2 Fig.3

/9] L3 I j 6 7 HISAYUKI MORI and YOJI NOGUCHI} INVENTORS d u! M ATTORNEY S Patented July 18, 1972 3,677,670

4 Sheets-Sheet 3 HISAYUKI MORI and YOJ I NOGUCHI,

INVENTOR s fllwlmni. 2,11 p ATTORNEYS Patented July 18, 1972 3,677,670

4 Sheets-Sheet 4 82 HISAYUKI MORI and YOJI NOGUCHI,

INVENTOR S BYIJMM; 2344i PM, ATTORNEY s ROTATIONAL MOLDING APPARATUS This invention relates to a rotational molding apparatus which is suitable for the mass production with good reproducibility of rotationally casted synthetic resin articles of good quality, in which the productive efficiency is improved and the control of production as well as heating temperature has been made easy. More specifically, the invention relates to a rotational molding apparatus comprising annular tracks, a plurality of drive carriagestraveling along said tracks, rotary molds coupled to said carriages through the intermediary of supporting means and detachable therefrom, rotatory mechanisms for transmitting a rotative motion from a drive source disposed in said several carriages to a rotating shaft of said several molds, a heating tunnel which houses a part of said annular tracks and permits the passage therethrough of said carriages and molds, and a cooling tank disposed in the pathway of the molds which emerge from said tunnel after passage therethrough, through which tank said molds pass while being cooled in the meantime.

The so-called rotational molding method is being widely used for molding hollow shaped articles of synthetic resin. In this method particulate or powdered synthetic resin is placed inside a rotary mold whose mold cavity coincides with the shape of the article desired, after which the mold while being rotated is heated to cause the molten resin to adhere to the inner surface of the mold and thereby impart shape to the synthetic resin, thus obtaining the shaped article of desired form. However, the productive efficiency was poor in the case of the conventional rotational molding method, since only one mold could be placed in the heating furnace at a time, and hence the number of units of the shaped articles that could be formed per unit time was very small.

Further, the mold is conveyed to a prescribed place in the furnace and undergoes a prolonged period of heating at this place. There were however the drawback in this case in that difficulty was experienced in controlling the temperature of the furnace. A prolonged period of time would be required for the molding operation if the temperature of the furnace was slightly lower than the melting temperature of the synthetic resin, whereas if this temperature is high, degradation of the resin would take place to result in impairment of the quality of the shaped article.

An object of the present invention resides in solving the foregoing drawback that was possessed by the conventional rotational molding apparatus and provide a rotational molding apparatus suitable for the mass production with good reproducibility of rotationally casted synthetic resin articles of good quality, this being achieved by the adoption of a continuous process for the molding of the shaped articles to thereby raise the production efficiency by increasing the productivity per unit time. Another object is to provide a rotational molding apparatus in which the productive process and the heating temperature are readily controlled. Other objects and advantages of this invention will be apparent from the following description.

The present apparatus, as previously described, includes annular tracks, a plurality of drive carriages, rotary molds coupled to the aforesaid carriages through the intermediary of supporting means, a mechanism for rotating the aforesaid mold, a heating tunnel and a cooling tank.

For a better understanding of the setup of the present apparatus, several embodiments of the invention will be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a first embodiment of the present invention;

FIG. 2 is a schematic side view of portions of the embodiment ofFig. 1;

FIG. 3 is an enlarged view of the carriage arrangement of the embodiment of Fig. l;

FIG. 4 is a schematic plan view of a second embodiment of the present invention;

FIG. 5 is a schematic side view of the heating tunnel of the embodiment of Fig. 4;

FIG. 6 is a top view of the arrangement of Fig. 5; and

FIG. 7 is a schematic side view of a modified mounting arrangement.

In FIGS. 1-3 an annular track I is provided supported overhead by means of supporting means (not shown), which per se is known, for example, posts, arms, etc. Track 1 is provided with a plurality of drive carriages 3, 3, for example elec trically driven carriages, which are mounted at suitable intervals along the track.

As regards the means of supporting the annular track and method of driving the carriages, these are well known in connection with dependent cable cars, dependent monorail cars and ski lifts, and those skilled in the art are well aware that various modifications indesign are possible.

Carriages 3, 3, have coupled thereto rotary moldy (2) (2), which being coupled through the intermediary of suitable supporting means are detachable from said supporting means. One mode of this carriage-mounted mold is shown in detail in FIG. 3 In FIG. 3 is shown a supporting means which has a dependent rotating shaft 6 coupled to and rotated by means of a drive source disposed in the carriage [a drive source 7], a rotating rack 5 secured to the shaft 6, and a mold mounting rack 4 fitted to the bottom of said rack 5 by means of a rotating attachment shaft 10. Thus, since the rotary mold 2 is detachably mounted in the rack 4, it becomes coupled to the drive carriage 3 through the intermediary of the foregoing supporting means.

In FIG. 3 the embodiment illustrated is one which uses an electrically driven carriage as the drive carriage. Carriage 3 is provided with wheel-carrying plates 31 which are fitted with wheels 8. Wheels 8 are rotatively driven by an electric current which has been collected from an overhead electric wire 20 by means of an electric current collector 34 and delivered via an electric current transmitting arm 19. Thus the carriage 3 is made to circle about the annular track 1. Further, the drive motor 7 for rotating the mold is also supplied with an electric current via the aforesaid electric current transmitting arm 19- and rotated thereby. In the embodiment shown in FIG. 3 there is provided a rotatory mechanism which transmits a rotational motion from the motor 7 disposed in the carriage to a mold rotating shaft 36, said rotatory mechanism comprising a belt 11, say a chain belt, which is mounted about a rotating shaft 9 of motor 7 and the hereinbefore mentioned rotating attachment shaft 10, and a gear mechanism for transmitting the rotation of the rotating attachment shaft 10 to the mold rotating shaft 36.

The hereinabove described rotatory mechanism merely il- Iustrates one mode of accomplishing the rotation of the mold. Modifications are possible by combining the rotating shafts, belt and gear mechanism in various ways. For example, the gear of rotating shaft 32 and that of rotating shaft 36 may be brought into direct engagement, or the rotating shafts 32 and 36 may be connected with a belt, or the shaft 36 may be rotated by rotation of the shaft 32. Hence, in the case of an apparatus of the type illustrated in FIGS. 1-3, it is to be understood that what is referred to herein as the rotatory mechanism, i.e., the mechanism which transmits a rotational motion from the drive source disposed in the several carriages to the rotating shaft of the rotary mold, comprehends numerous modification and variations in design for achieving the object of said rotatory mechanism so long as the rotation by the dependent rotating shaft 6 and the rotating rack 5 of the mold mounting rack 4 affixed to the lower part of the aforesaid rack 5 is not impeded.

In the apparatus of the type shown in FIGS. 1-3, since it is of a construction as illustrated in FIG. 3, the rotation of the drive source 7 causes the rotating shaft 6 to rotate and, as a result, the rotating rack 5 secured thereto is rotated which, in turn, rotates the mold mounting rack 4 thereby causing the mold 2 mounted in the rack 4 to rotate about the rotating shaft 6 in the direction of arrow b as shown in FIG. 3.

On the other hand, the mold rotating shaft 36 is rotated by the previously described rotating mechanism to rotate the mold 2 mounted in the mold carrying rack 4 in the direction of arrow a.

Thus, as described, the mold 2 can be made to travel about a peripheral course along the annular track 1 while being rotated in both the directions indicated by the arrows a and b.

In the invention apparatus of the type illustrated in FIGS. 1-3, various modifications in design are possible in achieving the support of the rotary mold in the supporting means in a detiachable manner. FIG. 3 shows one mode of achieving this en FIG. 3 illustrates the instance where the mold 2 by having its rotating shaft 13 joumalled in a hinged side 37 of the mold mounting rack 4 and the shaft 36 in a fixed side 38 in opposing relation to the foregoing side 37 is mounted detachably in said I rack 4. In this embodiment a rack side locking member 35 is used to secure the side 37 so as to make possible its opening and closing.

As possible modifications in supporting the rotary mold 2 detachably in the rack 4, the following may be used. For example, an electromagnetic mechanism can be employed and so adapted that when the shafts 13, 36 have arrived at the mounting position in the rack 4 the two sides 37 and 38 are closed by the action of the magnetic device to effect the insertion of the shaft 13, 36 in shaft mounting holes (not shown) provided in the two sides of the rack. Alternatively, a hydraulically or pneumatically operated device can be used to open or close the two sides 37 and 38 of the rack 4 and thus accomplis'h the mounting or dismounting of the shafts 13, 36 in the shaft mounting holes provided in the two sides of the rack 4. Further, the rotary mold shown in FIG. 3 is of a type which is made up of two members in the axial direction of the rotating shaft, i.e., one which can be separated into an upper mold 21 and a lower mold 22.

The present apparatus, in both cases of the type which has been described hereinabove and the type to be described hereinafter with reference to FIGS. 4-7, includes a heating tunnel 14 which housing a part of the annular track 1 permits the passage of the aforesaid mold 2 and carriage 3 therethrough and a cooling tank 16 which being disposed in the pathway of the mold 2 emerging from the tunnel cools the mold by it passing it through the coolant contained in the tank.

In FIG. 1 the reference numeral 12 denotes the material feeding stand at which the material synthetic resin is charged to the rotary molds 2. When a mold 2 passes atop the stand 12, the mold mounting shaft 13 which carries the mold 2 is released from the mold mounting rack 4, as shown in FIG. 3 by means of the broken line, and is split into an upper mold 21 and a lower mold 22 wherein the synthetic resin material is fed, after which the upper and lower molds 21, 22 are closed, the mold mounting shaft 13 is mounted in the mold mounting rack 4, and the mold 2, while making its hereinbefore described rotational motions in the directions of a and b as shown in FIG. 3, travels over its peripheral course by being conveyed by the carriage 3.

The mold 2, which travels through the heating tunnel 14 while being rotated, is heated by a suitable means of heating as by gas, electricity or infrared rays provided in the inside wall of the furnace. Thus, the material resin inside the mold 2 is melted in the heating tunnel to become adhered to the inside surface of the mold and thereby is imparted the shape that is desired in the product.

In carrying out this heating operation, it is preferred that the temperature of the heating tunnel 14 through which the mold 2 travels first is set at a temperature higher than the melting temperature of the resin material as this results in the rapid melting of the resin. On the other hand, the temperature of that part of the heating tunnel 14 through which the mold 2 travels last is preferably set at a temperature lower than the melting temperature of the resin material so as to result in a uniform shaping of the product.

As the cooling means to be used in the cooling tank 16, preferably used is a water bath or water shower. When a water bath is used, as shown in FIG. 2, the annular track 1 is so arranged that at this point the track is bent downwardly to ensure that the mold 2 is dipped into the water bath. The bending of the track 1 need not be adopted in the case the cooling water is applied by means of a shower.

In FIG. 1 the reference numeral 17 denotes the shaped article withdrawal stand. The mold mounting rack 4, which has traveled about its peripheral course on the annular track 1 while being rotated, completes the molding of the shaped article by passing through the heating tunnel l4 and cooling tank 16 and arrives at the shaped article withdrawal stand 17. At this stand the rack side locking member is unlocked and one side 37 of rack 4 is opened while the mold rotating shaft 36 is extracted from the other side 38 of rack 4 at the opposite side, and the mold 2 is removed from the mold mounting rack 4. The shaped article is then removed from the mold 2 by splitting it at the shaped article withdrawal stand 17. The shaped article withdrawal stand 17 and the material feeding stand 12 may be disposed adjacent each other without any spacing between the two stands.

Further, a belt conveyor 18 can be additionally provided for hauling away the shaped articles which are removed after completion of their molding by the molds 2.

Aside from the embodiment hereinbefore described with reference to FIGS. 1-3, there is an embodiment of the invention wherein the molds are mounted in drive carriages which travel over annular tracks laid on the ground.

One mode of this latter type is illustrated in FIGS. 4-7. In the embodiment shown the annular tracks consists of a plurality of annular tracks (in FIG. 4 two pair of rails are shown) a part of whose circuits are in common and having a switching mechanism at the point where the tracks branch off from the common portion. A single pair of rails can also be employed, however. Further while the figure illustrates the case where each consist of a pair of rails, a monorail car type carriage straddling a single rail can also be used for the annular tracks.

An invention apparatus of this type comprises one or more annular tracks laid on the ground [41 and 42 in FIG. 4], a plurality of drive carriages 49, 49, traveling along said tracks, at least two extensible supporting members 56, 56 provided in each of the aforesaid carriages, rotary molds 50 each of which by being detachably mounted to the top ends of the aforesaid supporting members is coupled to the aforesaid carriages through the intermediary of said supporting members, rotatory mechanisms each of which transmits a rotational motion to a rotating shaft 57 of each of the molds from a drive source 58 disposed in each of the aforesaid several carriages, heating tunnels 45, 46 which house a part of the foregoing annular tracks and permit the passage therethrough of the aforesaid carriages and molds, a mold mounting rack 66 joumalled rotatably in the two side walls of each of said heating tunnels and having rotating shaft hitching members 67, 67 adapted to engage the rotating shaft 57 of a rotary mold elevated by the extension of the aforesaid supporting members 56, 57, as well as a rotary mechanism [70, 71 and 72 in FIG. 6] for transmitting the rotational motion of said mold mounting rack 66 to the rotating shaft 57 of the rotary mold 50, and cooling tanks 47, 48 provided in the pathway of the molds which have passed through the respective tunnels and emerge therefrom, whereby the molds are cooled as they pass therethrough.

Annular tracks, one an annular track 41 of small perimeter and another an annular track 42 of greater perimeter are provided, the tracks 41 and 42 being made up by laying on the floor respectively pairs of rails 51, 52 and 61, 62 with a prescribed distance between the rails. A part of the periphery of each of the tracks 41 and 42 are in common, thus forming a common track part 43. The reference numeral 44 denotes an extension track which has been extended away externally of the annular tracks 41, 42 from one end of the common track 43. Annular tracks 41, 42 are each provided in opposing relationship to the common track 43 shown in FIG. 4, with respectively heating tunnels 45, 46 and cooling tanks 47, 48. Rotary mold 50 has formed in its interior a cavity having a configuration coinciding with the shape of the intended shaped article. For introducing the rotary mold onto the annular tracks 41, 42 the rotary mold 50 is mounted on the carriage 49 placed on the extension track 44, after which the carriage 49 is moved forward into the common track 43. A plurality of carriages 49 each mounted with a rotary mold 50 are moved onto the annular tracks 41 or 42 and are caused to travel peripherally about the annular tracks 41 or 42. Carriage 49 mounted with the rotary mold 50 is moved from the common track 43 onto either the annular tracks 41 or 42. For this purpose one of the hydraulically or pneumatically operated switching devices 53, 54, 55 is operated to switch the carriage 49 onto either the annular track 41 or 42. By the prompt operation of the switching devices 53, 54, 55 the carriage 49 can be moved onto both annular tracks 41 and 42 and thus make it possible to employed both tracks 41 and 42 in carrying out the molding operation.

Carriage 49 is provided with mold supporting members 56 which are extensible At the top end of the mold supporting members 56 are detachably mounted rotating shafts 57. A mold rotating motor 58 operates to rotate the rotating shaft 57 through the intermediary of shafts 59 and 60 to thereby cause the mold 50 to rotate about the rotating shaft 57. It is to be readily understood that the rotatory mechanism for transmitting the rotational motion from the drive source disposed in the several carriages to the rotating shaft 57 of the mold is not limited to the method hereinabove described but that modifications can be made in designing this mechanism, in which, for example, may be used a chain belt and gear mechanisms individually or suitably combined.

Carriages 49 are provided with wheels 63 which are rotated by means of an electric current collected via a power transmitting arm 64 from an electric wire 65 disposed below the annular tracks 41 and 42. Carriages 49 are thus adapted to travel peripherally on the annular track 41 or 42. Further, the electric current is also transmitted to the motor 58 for rotating the mold of the carriage 49 via the power transmitting arm 64 and thereby operates the motor 58 for rotating the-mold. Mold 50 which moves peripherally on the annular track 41 or 42 enters the heating tunnel 45 or 46 and is heated by means of the heat from a heat source 75 installed in the wall of the tunnel. While the heat source shown in FIG. 5 is electrical, other means of heating can be employed as in the case of the embodiment shown in FIGS. 1-3.

Although the rotary mold 50 shown in FIGS. 5 and 6 is of a type which is separable at right angles to the axis of rotation and closed by a closure fitting 73, the mold may also be of the split type mold shown in FIG. 3.

In FIGS. 5 and 6 the reference numeral 66 denotes a mold mounting rack. Mold mounting rack 66 is a quadrilateral framework provided in its two opposing sides with rotating shaft mounting means 67 which by being capable of mounting the rotating shafts 57 of mold 50 rotatably therein adapts the mold mounting rack 66 for receiving the rotary mold 511 which has been lifted by the extension of the mold supporting members 56.

As best illustrated in FIG. 6, the method employable for receiving and mounting in the rotating shaft mounting means 67 of rack 66 the rotating shaft 57 of mold 50, which has been lifted by the extension of the supporting members 56 in the heating tunnel, may be that wherein the mounting of the rotating shafts S7 in the rotating shaft mounting means 67 is accomplished by the mounting pins 78 becoming inserted into the pin insertion holes 79 of the rotating shafts 57 when the rotating shafts S7 arrive at the mounting position. For accomplishing the insertion of the mounting pins 78 in the insertion holes 79, useable is a method of moving the mounting pins electromagnetically or by of a hydraulic or pneumatic means. Alternatively, another mode of mounting that can be adopted is that wherein the rotating shafts 57 of the mold are rotatably supported in the two side walls of the heating tunnel by means of mold mounting rack rotating shafts 68 which are provided in the middle part of the other two opposing sides of the mold mounting rack 66 and hence effect the rotation of the mold along with the rack upon operation of the motor 69. For example, as another modification, the mode illustrated in FIG. 7 can be employed.

Referring to FIG. 7, a mold carrying stand 82 is elevated and lowered through the intermediary of a cable 81 by actuation of a pneumatically operated cylinder 80. When the mold carrying stand 82 is elevated to its upper limit, clutches 85, 86 provided in the rotating mold mounting rack (not shown) and shaft ends 88, 88 of the rotating shafts of the mold are brought into alignment. At the same time, a gear 83 provided in the mold carrying stand 82 engages with a gear 84 fitted to the rotating rack and causes the latter to be rotated. As a result, gear 84 and the integrally attached clutch 85 proceeds inwardly by a screwing action of the shaft on which the clutch 85 and the gear 84 are integrally attached to cause the clutch 85 to slip over the shaft end 88, and at the same time the shaft end 87 slips into clutch 86. At this point the mold carrying stand 82 starts its descent. On the other hand, when it is desired to lower the mold from the rotating rack, the clutches 84, 86 are retracted by reversing the screwing action of the shaft to which the clutch is attached by reversing the rotation of the gear 83. A rotation stopper 87 is provided at a point near the end of the rotating shaft to prevent free running to take place between the clutch 86 and the shaft end 87, this being accomplished by the stopper 87 slipping into grooves 86 provided in the clutch 86.

Reverting to FIG. 6, one mode of a rotatory mechanism for transmitting the rotational motion of the rotating shaft of rack 66 to the rotating shaft 57 is illustrated therein.

A rotating shaft 70 concentrically fitted in the mold mounting rack rotating shaft 68 is coupled to a motor 69 at its one end. Thus, when the rotating shaft 70 is rotated by the operation of the motor 69, a connecting shaft 72 is rotated by a chain 71 as a result of the rotation of the shaft 70 and, in turn, the rotary mold 50 is rotated about the rotating shaft 57 mounted in the rotating shaft mounting means 67. It will be readily understood by those skilled in the art that various modifications in design are possible in the case of the foregoing rotatory mechanism by suitably employing belts, e.g., a chain belt, gears and rotating shafts.

Hence, the mold 50 mounted in the mold mounting rack 66 is submitted to two rotations, i.e., a rotation means of the mold mounting rack rotating shaft 68 and a rotation by means of the rotation of the rotating shafts 57 of mold 50. When the mold 50 completes its prescribed rotation, the mold supporting members 56 extend upwardly and contact the rotating shafts 57 of mold 50, following which the shafts 57 are disengaged from the rotating shaft mounting means 67 to be again supported by the mold supporting members 56, while the mold 50 is again caused to be rotated about the rotating shafts 57 by means of the motor 58 located in the carriage 49. The carriage 49 then starts moving and proceeds from either heating tunnel 45 or 46 to either the cooling tank 47 or 48.

In cooling tanks 47 and 48 the mold 50 is cooled by a spray of cooling water. A

Thus the mold 50 makes its peripheral travel passing successively through the heating tunnel 45 or 46 and cooling tank 47 or 48 that are provided in the course covered by the annular tracks 41, 42.

The reference numeral 76 denotes the feed stock charging port from which the thermoplastic resin is charged to the inside of the mold 50. When the mold 50 passes this point, it is split and fed with the starting thermoplastic resin, after which it is again closed and made to travel about its peripheral course on the annular track 41 or 42.

The mold 50 which has completed the molding of a product by being rotated while traveling about the peripheral course on either the annular tracks 41 or 42 and passing through the heating tunnel 45 or 46 and the cooling tank 47 or 48 is split open at a shaped article withdrawal stand 77 and the resulting shaped article is removed.

Thus, in the case of the rotational molding apparatus according to the present invention it is possible to provide an annular track overhead and have carriages traveling on said track while depending therefrom, as illustrated in FIGS. 1-3, or lay the annular track on the floor and have the carriages travel on said annular track laid on the floor, as illustrated in FIGS. 4-7.

Further, although an extension track is not shown in the case of rotational molding apparatus illustrated in FIGS. 1-3, an extension track extending away externally of the annular track may be provided in this case also.

Thus, the desired shaped articles are obtained by the present rotational molding apparatus in the following manner. A plurality of molds are mounted on the annular track, which molds in making their travel about the peripheral course on the annular track are heated in a heating tunnel whereby the resin inside the molds is melted and by being adhered to the mold surface is imparted the shape intended. The resulting shaped articles are then cooled and solidified by passing through a cooling tank and thereafter withdrawn from the molds at a suitable point along the annular track. The molds are then charged with the starting resin and the operation is repeated.

Hence, as hereinbefore described, the series of molding steps consisting of charging the mold with the starting synthetic resin, molding, cooling and withdrawal of the shaped article can be carried out continuously and repeatedly while the molds make their peripheral travel about the annular track.

Since it is possible to mount a plurality of molds on the annular track in the case of the present rotational molding apparatus, a plurality of shaped articles can be molded continuously. In consequence, the time required for molding each article is notably shortened as compared with that of the conventional rotational molding apparatus.

Further, since a heating tunnel is provided along the annular track in the present rotational molding apparatus and the mold travels from one end of this tunnel to the other end thereof, a suitable gradient in temperature can be provided from one end of the heating tunnel to its other end. Hence, this makes it possible to control the temperature during molding, with the consequence that molding of shaped articles of good quality can be achieved.

When a rotational molding apparatus according to the present invention is provided with a plurality of annular tracks which have a part of circuits of the several tracks in common and each of said plurality of annular tracks is provided with its own heating tunnel and cooling tank, the sizes of which heating tunnels and cooling tanks are varied, it becomes possible to employ the annular track provided with a heating tunnel and cooling tank which is suitable for the shape and dimension of the mold to be used. Hence, such troubles asinsufficient melting of the resin due to the distance between the heat source in the heating tunnel wall and the mold being too great or the inability to obtain shaped articles of uniform quality due to localized heating of that portion near the heat source as a result of the distance between the heat source and the mold being short can be avoided. Consequently, the heating of the mold can be carried out adequately and uniformly thereby yielding products of uniform quality.

Further, since the plurality of annular tracks each have a part of their circuits in common, the steps of charging of the starting material to the inside of the mold and withdrawing the resulting shaped articles can be carried out at the part where the annular tracks are in common to make it unnecessary to carry out these steps in each of the annular tracks, thus making it possible to carry out the steps of charging the starting material and withdrawing the resulting shaped articles with efficiency.

When the rotational molding apparatus is one according to the invention having an annular track on which are mounted a plurality of molds and further provided with an extension track extending away externally of the annular track and is so adapted that the aforesaid molds can move along either the annular track or the extension track, the molds to be introduced onto the annular track can be done so from the extension track and, in addition, in case where a mold can no longer be used due to breakdown, it can be withdrawn via the extension track. Now, if the apparatus is one consisting of a plurality of annular tracks having a part of their several circuits in common and an extension track is provided extending away externally of one end of the circuits in common, a single extension track will serve the purpose of introducing the molds onto the several annular tracks or withdrawing the molds therefrom even when a plurality of annular tracks have been provided.

We claim:

1. A rotational molding apparatus comprising at least one annular track, a plurality of separate and distinct drive car riages movable along said track, means for moving said carriages along said track, a rotary mold supported by supporting means coupled to each of said carriages through the intermediary of said supporting means, and individual drive source positioned in each of said carriages, rotary mechanism means operably connected to each of said drive sources for transmitting rotational motion to a rotating shaft of each of said molds from said drive sources, a heating tunnel for each of said annular tracks, said tunnel housing a part of said annular track and permitting the passage therethrough of said carriages and molds, and a cooling tank for each of said annular tracks, said cooling tank being provided in the path of said molds as they emerge from the heating tunnel after passage therethrough said cooling tank being adapted to cool said molds as they pass therethrough.

2. An apparatus according to claim 1, wherein said at least one annular track is supported from above, said supporting means each including a dependent rotating shaft rotated by said drive source disposed in each of said several carriages, a rotating rack secured to said rotating shaft, and a mold mounting rack fitted to the lower part of said rotating rack by means of a rotating attachment shaft, said molds comprising rotary molds each of which is detachably mounted in said mold mounting rack and thereby coupled -to each of said carriages.

3. An apparatus according to claim 1, wherein said at least one annular track is laid on the ground, said supporting means comprising at least two extensible supporting members provided in each of said carriages, said molds comprising rotary molds each of which is detachably mounted to the top ends of said supporting members and thus coupled to said several carriages through the intermediary of said supporting members, a mold mounting rack journalled rotatably in two side walls of said heating tunnel and having rotating shaft hitching members adapted to engage said rotating shaft of a rotary mold elevated by the extension of said supporting members, and a rotary mechanism for transmitting the rotational motion of said mold mounting rack to the rotating shaft of the rotary mold.

4. An apparatus according to claim 2 wherein each of said rotatory mechanism means comprises a belt connecting said drive source and said rotating attachment shaft and a gear mechanism for transmitting the rotation of said rotating attachment shaft to said rotating shaft of said mold.

5. An apparatus according to claim 2 wherein said rotary mold is a split mold capable of being split in the rotational axial direction, the rotating shaft of said mold at its one end being journalled in a hinged side of said mold mounting rack, the other end of said rotating shaft being journalled in a fixed side of the rack in opposite relation to said hinged side, whereby said rotating shaft is mounted detachably in said mold mounting rack.

6. An apparatus according to claim 2 wherein said annular track has an extension track externally extending away from a part thereof.

7. An apparatus according to claim 3 wherein said annular track has an extension track externally extending away from a part thereof. 

1. A rotational molding apparatus comprising at least one annular track, a plurality of separate and distinct drive carriages movable along said track, means for moving said carriages along said track, a rotary mold supported by supporting means coupled to each of said carriages through the intermediary of said supporting means, and individual drive source positioned in each of said carriages, rotary mechanism means operably connected to each of said drive sources for transmitting rotational motion to a rotating shaft of each of said molds from said drive sources, a heating tunnel for each of said annular tracks, said tunnel housing a part of said annular track and permitting the passage therethrough of said carriages and molds, and a cooling tank for each of said annular tracks, said cooling tank being provided in the path of said molds as they emerge from the heating tunnel after passage therethrough said cooling tank being adapted to cool said molds as they pass therethrough.
 2. An apparatus according to claim 1, wherein said at least one annular track is supported from above, said supporting means each including a dependent rotating shaft rotated by said drive source disposed in each of said several carriages, a rotating rack secured to said rotating shaft, and a mold mounting rack fitted to the lower part of said rotating rack by means of a rotating attachment shaft, said molds comprising rotary molds each of which is detachably mounted in said mold mounting rack and thereby coupled to each of said carriages.
 3. An apparatus according to claim 1, wherein said at least one annular track is laid on the ground, said supporting means comprising at least two extensible supporting members provided in each of said carriages, said molds comprising rotary molds each of which is detachably mounted to the top ends of said supporting members and thus coupled to said several carriages through the intermediary of said supporting members, a mold mounting rack journalled rotatably in two side walls of said heating tunnel and having rotating shaft hitching members adapted to engage said rotating shaft of a rotary mold elevated by the extension of said supporting members, and a rotary mechanism for transmitting the rotational motion of said mold mounting rack to the rotating shaft of the rotary mold.
 4. An apparatus according to claim 2 wherein each of said rotatory mechanism means comprises a belt connecting said drive source and said rotating attachment shaft and a gear mechanism for transmitting the rotation of said rotating attachment shaft to said rotating shaft of said mold.
 5. An apparatus according to claim 2 wherein said rotary mold is a split mold capable of being split in the rotational axial direction, the rotating shaft of said mold at its one end being journalled in a hinged side of said mold mounting rack, the other end of said rotating shaft being journalled in a fixed side of the rack in opposite relation to said hinged side, whereby said rotating shaft is mounted detachably in said mold mounting rack.
 6. An apparatus according to claim 2 wherein said annular track has an extension track externally extending away from a part thereof.
 7. An apparatus according to claim 3 wherein said annular track has an extension track externally extending away from a part thereof.
 8. An apparatus according to claim 7 wherein said at least one annular track comprises a plurality of annular tracks a part of the circuits of which are in common, said tracks being provided with track switching mechanisms at the junctions from which the tracks branch off from the common part. 